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I've definitely carried artwork of that size onto an aircraft, but it was a single painting and on the one occasion, where it was in a frame, I removed the frame to bring down the size. I simply wrapped it in small bubble wrap and put it in a reusable supermarket bag. I have no idea how many works you are planning to bring, but I'd imagine you'll have a problem with more than three or four. Also, s
me aircraft do not have closets or overhead bins that will accommodate something that is as big as 20x24. You'll need to do some planning if you don't want to roll these up for transport or pack them well and check them in as baggage.